Prior art rust removers generally contain high concentrations of phosphoric acid. The use of phosphoric acid in these products presents several disadvantages. Since phosphoric acid is such a strong acid, it must be handled with caution, and therefore may be disadvantageous for use in consumer products. Rust removers containing phosphoric acid are generally applied using rubber gloves and the additional use of rubber aprons is frequently recommended. In addition, phosphoric acid disposal is a problem in products which are rinsed with water. Phosphates enter the environment and are known to cause or accelerate algae bloom. Further, since phosphoric acid is a strong acid, its corrosive effects do not stop completely at the surface of the metal after the rust has been removed. Overexposure of the metal to a phosphoric acid containing product can cause damage to the metal surface.
Other prior art rust removers contain sulfuric acid in combination with phosphoric acid. The sulfuric acid is stronger and more corrosive than the phosphoric acid, and thus these combination rust removers present even more hazards than with phosphoric acid alone.
Other prior art rust removers contain oxalic acid as the main active ingredient. Oxalic acid is also caustic and corrosive to the skin, and is highly toxic upon ingestion.
While most prior art rust transforming compositions require the use of one or more very caustic ingredients, a number of anti-corrosive compositions have been produced using relatively mild ingredients. U.S. Pat. No. 3,173,864 to Freedman discloses water treatment anti-corrosion compositions which contain a combination of a water-soluble lignosulfonate and a chromate salt. The composition may additionally contain organic acids, such as citric acid, gluconic acid or ethylene diamine tetra-acetic acid.
U.S. Pat. No. 3,639,278 to Hwa discloses a scale removing and inhibiting composition containing lignosulfonic acid and glycolic acid.
U.S. Pat. No. 3,766,077 to Hwa et al discloses scale-inhibiting compositions comprising lignosulfonic acid or sulfonates and water-soluble organic polymers.
U.S. Pat. No. 4,529,450 to Panayappan discloses a metal oxide removing composition which contains a water soluble polymer, erythorbic acid, a surfactant, a buffer, and optionally ascorbic acid and citric acid. The composition is one adapted to be sprinkled as a powder onto a wetted oxidized surface and then rinsed off or dissolved in water and applied to the metal surface. The powder or aqueous solution, however, are not very suitable for application as a coating, especially to a vertical surface.
As stated above, these compositions contain less caustic components than prior art rust removing compositions and the components have the added advantage of being more environmentally compatible upon disposal. Thus, it would be advantageous to produce a rust conversion and removing composition containing less caustic, environmentally stable components than prior art rust conversion compositions which are useful even when applied to a vertical surface.